Solar concentrators, having round and cylindrical parabolic concave mirrors, which concentrate the sun's rays on an absorber surface from which the heat produced is transferred, are already known, see Matthofer, "Sonnenenergie", Umschau-Verlag, Frankfurt/M., 1976, page 256. These devices have many parts, are difficult to operate, are difficult to build and are very large and very costly to manufacture. The mirror surface becomes dirty very quickly and is difficult to clean and also becomes scratched through constant cleaning. The units cannot be produced by mass production techniques.